Self-moving carts are known, provided with small independent motors (electric-battery motors, small combustion engines, . . . ), which are employed for transporting objects or work/sport equipment on rough terrain, in the presence of an operator who walks alongside controlling speed and direction thereof. A particularly widespread application, on which the following description will be mainly based, is that of golf caddies, that is electric-drive caddies for transporting golf bags.
Golf caddies are normally provided with three or four support wheels, of which the driving one/s are controlled by one or two (in order to have two independent motor shafts) battery-powered electric motors. These caddies are conceived to save the golf player from carrying on his/her shoulder his/her bag containing the clubs and all the items required for playing (balls, tee, . . . ), which may weigh up to 20 kilograms, along the various kilometers which are walked when completing a golf game.
Although motorless carts also exist, self-moving ones have an undeniable advantage, as they save the golf-player from the effort of pushing or dragging the cart on usually rough and sometimes muddy and irregular playing fields.
The self-moving golf caddie is essential for people who would not be strong enough to carry along or push the golf bag and in any case it is very useful also for those who would have the physical strength but who can save energies for the game.
However, the provision of a drive on golf carts implies various problems. One of the most significant ones is that of adjusting the caddy speed to adapt it to that of the moving player, in particular because he/she continuously accelerates, slows down and stops on the golf course, both to play when it is his/her turn, and to wait for game companions when it is their turn.
In substance, as it can be guessed, a significant problem of self-moving carts is that of causing them to follow the movements of the respective player in as regular a way as possible.
A first type of known cart, of a simpler and cheaper construction, provides a manual control device arranged on the guiding handle. Thereby, the player always maintains contact with the caddy handle, which enables him/her to guide the movement direction, so he/she can simultaneously act on the controls which are mounted on the handle, within easy reach. In this case, the control device comprises at least a switch, to switch the motor on and off, and a speed adjuster, usually in the shape of a small wheel or other mechanical device which acts on motor speed.
This solution is inexpensive and reliable, also because the player always maintains caddy guidance, but the adjuster requires continuous and meticulous handling, to adapt the caddy pace to the player's, which is at least inconvenient. Moreover, in case a mistake is made in adjusting the speed (humidity may cause contact with the adjuster to become slippery) or contact with the caddy is lost (for example due to a snag), caddy control may be lost, with the risk of damaging the golf course or the equipment.
Summing up, this control mode causes an unpleasant distraction to the player and problems for the speed setting and possibly for the direction to be imparted to the caddy, which must be continuously manually adjusted.
As electronics costs and dimensions drop and as the calculation power of electronic circuit boards increases, it has been possible to offer semi-automatic or fully automatic golf caddies; they solve the problems set forth above, moving independently on the ground, without physical contact being required between the player and the caddy and without the player having to actively set the caddy speed.
All the solutions known so far start from the approach that the cart must follow the player during his/her movements on the golf course. Therefore, the control system provides a receiver/transmitter, two-unit apparatus, partly mounted onboard the cart and partly carried by the player. The two units exchange signals transmitted through the air (on various wavelengths and with various powers, depending on the circumstances) so that the relative position thereof may be determined and a control may be sent to the cart drive to follow the unit which the player carries with him/her. Examples of these known systems are described in U.S. Pat. No. 3,742,507, U.S. Pat. No. 3,472,333, U.S. Pat. No. 3,812,929, U.S. Pat. No. 4,844,493, U.S. Pat. No. 5,611,406, U.S. Pat. No. 5,711,388, WO201359423, EP2021823.
In some cases it is also resorted to a player's position signal detected with GPS technology.
However, all these solutions, in which the cart follows the player, imply a variety of problems:
a. the transmission system and the track-and-follow logic is expensive to accomplish and necessarily requires an electro-mechanic steering system or double motor for changing direction, because the cart is independent and must be able to steer automatically;
b. the control system is not applicable to existing manual carts, but at a higher cost than the cart itself;
c. The player is forced to carry with him/her a control unit which identifies him/her univocally, to allow the cart to follow the correct player; the individual portable units must hence be always maintained with the relative cart or preliminary programming to the use of the cart must be made by the user, which is certainly a problem in large golf clubs (where a plurality of carts are always kept at the players' disposal);
d. cart independence may lead it to go through not-allowed areas (such as the greens and the bunkers), narrow passages (small bridges, bottlenecks, . . . ) or bumpy paths (potholes, soft ground, . . . ), with the imaginable consequences;
e. the following distance, with which these systems work best, may cause the cart trajectory to intercept obstacles or other players;
f. if the cart stops due to an obstacle (a rock, a ditch, yielding ground, . . . ), the player does not realise it immediately and may walk away by a fair distance before having to walk back to collect the equipment.
Other proposed solutions for directing and moving golf carts at controlled speed provide to act with a traditional remote “guiding” system, that is, through a remote control (see for example U.S. Pat. Nos. 3,472,333, 3,720,281, 3,742,507, 3,812,929, 3,856,104, 3,976,151 and 4,109,186). In this case some of the problems illustrated above are solved, but the further problem of the difficulty of use is introduced.
Another disadvantage which all these track-and-follow or remote-control systems share is the fact that the user no longer comes into physical contact with the cart during the movement thereof. That fully removes a possible dragging effect, which some player has learnt to exploit, that is, the opportunity of being partly dragged by the cart, using the traction power of the wheels, especially when raised sloping areas must be approached.
An alternative consists in carts provided with proximity sensors facing towards the rear travelling side, that are moving preceding the player who follows. An example of these technical solutions is disclosed in FR2868560.
However, the control mode of the known solutions is not satisfactory yet. In particular, the use of some types of sensors does not provide a fully reliable signal, which makes these systems virtually unusable in practice.
Firstly, in order to propose a commercially acceptable system, it is necessary to employ modestly-priced sensors, which intrinsically provide signals subject to errors and disturbances; since cart control is rather critical, in order to be able to precede in a regular way the player at a short distance, any assessment mistake may lead to an unpleasant dynamic behaviour. In particular, prior-art systems are subject to control instability (elastic effect) which prevent the cart from synchronising with the player's speed.
Moreover, operation limits exist linked to the nature of the sensors.
For example, when the sensor is of the sonar type (that is, ultrasound), false readings may occur in case of strong wind, ice, dust, and/or high-pitched background sounds, which may gripper the uncontrolled start of the cart (safety problems). Moreover, when the user wears sound-absorbing garments (such as sponge-like piles or thick woolen jumpers, the sonar sensor does not correctly detect the distance and the cart does not move at all or very irregularly (movement smoothness problems). If the garments are loose or not perfectly perpendicular to the sensor, the sensor may detect measurements which differ up to 10 cm from the actual one. Finally, should the user move only his/her hand close to grab the cart handle, the ultrasound sensor may detect a general sudden approaching of the player and suddenly accelerate cart speed in an undesired manner.
When instead the sensor is of the infrared type, false readings easily take place depending on the temperature of the surrounding objects; on golf courses, outdoors, it is very likely that an infrared sensor is hit and saturated by direct sunlight, which produces an incorrect signal and imposes undesired movements to the cart.